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Proceedings of IPAC'10, Kyoto, Japan

frame design to provide support and alignment of the coldmass similar to that used for the SNS and 12 GeV upgradecryomodules, see figure 8. A test of this design with beamwould validate the HOM damping properties of thecavities and demonstrate operability in a configurationthat is very close to a production-ready environment.Plans for such a test are presently under discussion. Thisdesign could be used for a fourth generation light source.

Fig. 7. Concept for a high-current test cryounit.Fig.8. Cross section of high-current test cryounit showinghelium circuit, space frame and support rods.NEW APPLICATIONSThere is increasing interest in high-current capablecavities and cryomodules for hadron machines such asproton drivers (e.g. for neutrino physics), spallationneutron sources, and accelerator driven subcriticalreactors. Many of these machines are proposed to be CWor high duty factor with high average currents. Prospectsare good that such machines could be built in the nearfuture [3]. The JLab high current cavity concept could bea good candidate for such machines. It has a large bore,which is beneficial for minimizing beam halo interceptionas well as providing good cell-to-cell coupling. This tendsto minimize distortion of the field flatness due tomanufacturing tolerances or other detuning effects.However a smaller bore could yield greater efficiency,which is very important for CW applications, and there ispotential for a tradeoff in these respects.

Different FrequenciesThe concept can easily be scaled to differentfrequencies and this exercise has been performed forseveral potential applications from 650 MHz to 2.45 GHz.However it is not always optimal to simply do ageometric scaling as the resulting iris diameter may beunnecessarily large at the low end and unreasonably smallat the high end. Also the number of cells and strength ofHOM coupling are strongly application dependent.Low-beta applicationsThe high current cell shape has been scaled to a numberof different beta values from 0.65 to 1 [2]. In this scalingit is important to preserve the flat outer profile of the cellthat gives low tendency for multipacting. One example isshown in figure 9, using an SNS-style helium vessel andcoupler for illustration.Fig. 9. High-current 650 MHz 3=0.9 cavity conceptCONCLUSIONSAlthough the original high-current FEL application atJLab has gone away there is still interest in this conceptfor other applications from high brightness electroninjectors to high power CW proton drivers. The designscan be easily scaled to different frequencies and betavalues and adapted to specific HOM dampingrequirements. A beam test of this concept would be veryuseful in validating the impedance characteristics,especially above the beam pipe cut-off frequency.REFERENCES[1] F. Marhauser et.al., "JLab High-Current CryomoduleDevelopment", Proc. ERL09, Cornell University,2009.[2] R.A. Rimmer, F. Marhauser, "A Family of L-BandSRF Cavities for High Power Proton DriverApplications", Proceedings of PAC09, Vancouver,BC, Canada 2009.[3] R.A. Rimmer, "Prospects for a Very High Power CWSRF Linac", Proceedings of the Workshop onApplications of High Intensity Proton Accelerators,October 19-21, 2009 Fermi National AcceleratorLaboratory, Batavia, IL, USA, published by WorldScientific.